Load alleviation may be used to reduce bending moments at roots of wing boxes. Reducing the bending moments, in turn, enables wing box weight to be reduced. A reduction in wing box weight is highly desirable, as it reduces fuel costs and other aircraft operating costs.
Root bending moments may be reduced by unloading aerodynamic lift at tips of the wing boxes. Wing boxes of the Boeing 747 aircraft, for instance, are designed with a combination of high aft sweep and sufficient flexure to reduce wing tip angle of attack. Such passive load alleviation is generally lighter and less complex than active load alleviation. Active load alleviation may include actuators, flaps and other flight control mechanisms that add complexity and weight to the aircraft.
Wing boxes of certain future aircraft, however, might have lower sweep and flexure. For those future aircraft, other ways of passively reducing root bending moments are needed.